The construction of large-scale dams has played a surprising role in limiting rising seas, say scientists. Over the past century, melting glaciers and the thermal expansion of sea water have driven up ocean levels. But this new study finds that dams almost stalled the rising seas in the 1970s because of the amount of water they prevented from entering the oceans. Without them, the annual rate of rise would have been around 12% higher.
Measuring how much the seas have risen over the past 100 years or so is a difficult task for scientists. Researchers found that there was a gap between how much water they knew had gone into the oceans compared to how much those oceans had actually risen by over the past century. In this new work, the authors revisited information about sources and measurements to come up with a new, more accurate estimation. The study finds that overall sea level has risen by approximately 1.56mm per year between 1900 and 2018. The largest contributors to rising seas over most of the 20th century have been melting glaciers which have responded faster to a warmer world. Over this whole period, the authors believe that sea level would have been around 12% higher without the influence of dams and reservoirs.
However, the influence of dams in holding back the waters began to fade in the 1990s. Concerns were growing about the environmental impact of large dams, and the number of projects began to decline. At the same time, the growing influence of climate change spurred an increase in sea levels through increased ice loss from Greenland and greater thermal expansion of the waters as more heat energy went into the oceans. All these factors have seen the rise in sea levels accelerate over the past 30 years and it is now running at 3.35mm per year.
Source: BBC
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